There are a number of technologies existing today for displaying 3D images to multiple viewers. Generally, these technologies are implemented in locations where a large number of viewers will pass through, and often pay for the 3D experience. These locations include movie theatres, science centers and the like. To-date, there is no commercially available 3D display for use in the home. Since the amount of 3D content is currently limited, there is not a large market at the present for a dedicated 3D display for home use. To open up the 3D market for home entertainment, a 2D/3D switchable display is needed.
The available technologies for displaying 3D images include 3D model rendering, stereoscopic, volumetric and holographic. One of the most popular and longest-lived is stereoscopic, which has the subcategories of stereo-with-eyewear and autostereoscopic. The category stereo-with-eyewear is frequently assumed when the term stereoscopic is used, and the term autostereoscopic is used to mean explicitly that no eyeglasses are required to see the 3D image. The 3D display or stereoscopic display of images usually entails viewing on one and the same device a series of images corresponding to the right eye and a series of images corresponding to the left eye of an observer. These two video sequences are in general captured or generated in such a way as to make it possible to comply with the geometry of human vision so that the offsets between the left view and the right view of the observer are reconstructed correctly by the visual system, producing stereo vision.
There are a number of autostereoscopic technologies in development that are 2D/3D switchable. For example, U.S. Pat. No. 7,050,020 B2 describes a liquid crystal display unit with first and second lenticular lenses. To display a 3D image, the first lenticular lens is arranged such that its optical axis coincides with the optical axis of the second lenticular lens, allowing pixels for left and right eyes to display images for their respective eyes. To display a 2D image, the first lenticular lens is arranged such that its optical axis is shifted from the optical axis of the second lens by half a pixel pitch, allowing the pixels for the left eye and right eyes to display the same image independently. In another example, U.S. Pat. No. 7,199,845 B2 describes a switching type liquid crystal display device that includes a liquid crystal panel to activate and deactivate a parallax barrier to switch between a 2D and 3D image display mode. Further, U.S. Pat. No. 7,265,902 B2 demonstrates a display apparatus containing a light shielding plate and a light deflection plate. The light shielding plate switches so as to allow the light deflection elements to provide, or not provide, a 3D display mode. Unfortunately, these approaches are complex and expensive to manufacture, and the image quality is poor in 3D viewing mode, due to well-known difficulties in the angular dependence of the light modulation mechanisms in such technologies. Further, these technologies require the movement or alteration of physical structures inside the device to switch between 2D and 3D viewing modes.
There are four primary technologies for 2D/3D switchable displays in the category of stereo-with-eyewear, hereafter simply, stereoscopic. In all cases, the viewer is presented with a “left eye” and a “right eye” image. The first technology presents alternating left eye and right eye images that are electronically synchronized with LCD shutter glasses such that the lens over the left eye is transparent only when the left eye image is shown and vise-versa. A number of US patents in this field have issued to Lipton et al. (assigned to StereoGraphics Corporation), such as U.S. Pat. Nos. 4,523,226, 4,967,268, 5,181,133 and 5,572,250. However, the electronics for driving a 3D display using shutter glasses are complex. Also, the perceived luminance of the display is approximately half of that obtainable if the same system were used for 2D display, since only one eye is viewing at any given time in the 3D mode. The second technology is known as anaglyph, and the separation is accomplished by two broad color filters worn as glasses (typically red-blue), which correspond to the left eye/right eye image content. Anaglyph has a significant amount of color-cross talk and has many objectionable image artifacts. U.S. Pat. No. 4,290,675 by Besser describes one version of a 2D/3D switchable anaglyph display system.
The third and fourth stereoscopic technologies use passive glasses with alternating left eye, right eye image presentation. The third technology defines the image content by polarization, and the corresponding glasses have a left lens of opposite linear polarization than the right lens. Often, these polarization systems use two imaging paths where the two paths are combined by polarizing one of these two paths in a first specified orientation and by polarizing the other path in a second orientation. The glasses allow the user to view the combined 3D image. These polarization systems can be flat panel or are more often projection type. Projection systems use a special polarization preserving screen, which considerably raises the complexity and cost of such devices. Additionally, projection systems tend to have low luminance; each eye views only one polarization so the best case scenario would be a luminance of half of the available light. Furthermore, projection systems have polarization cross-talk since the polarizing glasses and internal polarizing means are not lossless.
The fourth technology is a passive filter technology using interference filters to separate the images by wavelength, or spectral bandpass. This technology was developed by DaimlerChrysler AG, and in 2003 Infitec GmbH emerged to commercialize the technology. The workings of the Infitec system can be easily understood with respect to “INFITEC—a new stereoscopic visualisation tool by wavelength multiplex imaging,” by H. Jorke and M. Fritz, Proceedings Electronic Displays September 2003, Wiesbaden. The publication of this paper can be found on the Infitec website (http://www.infitec.net/infitec_english.pdf). To date, this filter system has been exclusively utilized in projection applications. A projector using a broadband light source includes a color filter wheel having left and right image interference filters. The viewer wears passive glasses with filters of spectral bandpass corresponding to that of the filter wheel. Much like the polarization method, the luminance of these systems is low due to the inefficient use of the projector light by the filters. It has been proposed that the Infitec system would work best as a projection systems using laser sources, however, this is not known to have been actually implemented in practice.
Although all of the above 3D technologies are switchable to 2D displays, the aforementioned systems have been optimized for 3D performance. The corresponding 2D displays for each of the aforementioned technologies, typically have a 2D display with similar color gamut, efficiency and power consumption to that of currently available 2D systems. Additionally, with the exception of the Infitec system, all of the 3D technologies above use only broadband light sources, and are not designed for sources with narrow emission spectra. For the Infitec system, filtering of a broadband source to create two sets of primaries does not impart any benefit for 2D operation over that of a conventional display. Additionally, it has been suggested that for hypothetical 3D systems using 6 narrow emitters, such as lasers, the placement of the emitters would be close together in order to reduce the image processing needed for 3D. Placing the corresponding primaries near each other needlessly limits the 2D performance in a 2D/3D switchable display system.
There are 2D only display systems that have been described having more than six emitters. The additional emitters are employed for a variety of reasons, including improving luminance or color gamut. Generally these systems are not suitable for 3D display by wavelength segregation since the position of the emitters would not allow for the division of these six or more emitters into filterable groups of emitters.
A few projection solutions have been proposed using more than three-color light sources. However, the bulk of solutions proposed have not targeted color gamut expansion. Disclosures of projectors using more than three-color sources include U.S. Pat. No. 6,280,034 by Brennesholtz, which discloses a projection apparatus using up to six colors, employing RGB as well as CMY (cyan, magenta, and yellow) colors that are obtained from a broadband light source. Although such an approach may be useful to enhance brightness and luminance for some colors, the addition of complementary CMY colors does not expand the color gamut and, in practice, could result in a smaller color gamut, as indicated in the disclosure of U.S. Pat. No. 6,280,034. Additionally, the embodiment disclosed in U.S. Pat. No. 6,280,034 uses light sources having different polarizations, which prevents use of an analyzer for improving contrast.
U.S. Pat. No. 6,769,772 by Roddy et al describes a six color projection display system with increased color gamut. However, the embodiments disclosed in U.S. Pat. No. 6,769,772 teach against using two different red emitters, and therefore would not be suitable for use in 3D applications using spectral selection. Roddy et al. concern themselves with maximizing the 2D gamut of their particular projection display apparatus; they do not consider the use of the six emitters in alternative or non-projection systems.
Patent Application WO 01/95544 A2 by Ben-David et al. also discloses a display device and method for color gamut expansion using four or more substantially saturated colors. While the disclosure of application WO 01/95544 provides improved color gamut, however, the embodiments and methods disclosed apply conventional solutions for generating and modulating each color. The solutions disclosed use either an adapted color wheel with a single spatial light modulator or use multiple spatial light modulators, with a spatial light modulator dedicated to each color. When multiplexing a single spatial light modulator to handle more than three colors, a significant concern relates to the timing of display data. The spatial light modulator employed must provide very high-speed refresh performance, with high-speed support components in the data processing path. Parallel processing of image data would very likely be required in order to load pixel data to the spatial light modulator at the rates required for maintaining flicker-free motion picture display. It should also be noted that the settling time for conventional LCD modulators, typically in the range of 10-20 msec for each color, further shortens the available projection time and thus constrains brightness. Moreover, the use of a filter wheel for providing the successive component colors at a sufficiently high rate of speed has further disadvantages. Such a filter wheel must be rotated at very high speeds, requiring a precision control feedback loop in order to maintain precision synchronization with data loading and device modulation timing. The additional “dead time” during filter color transitions, already substantial in devices using 3-color filter wheels, further reduces brightness and complicates timing synchronization. Coupling the filter wheel with a neutral density filter, also rotating in the light path, introduces additional cost and complexity. Although rotating filter wheels have been adapted for color projection apparatus, the inherent disadvantages of such a mechanical solution are widely acknowledged. Further, without some shuttering means, color crosstalk becomes a problem. Color crosstalk occurs, for example, at a transition of light color while the corresponding data transition is also in process. Alternative solutions using a spatial light modulator dedicated to each color introduce other concerns, including proper alignment for component colors. The disclosure of application WO 01/95544 teaches the deployment of a separate projection system for each color, which would be costly and would require separate alignment procedures for each display screen size and distance. Providing illumination from a single light source results in reduced brightness and contrast. Moreover, the added cost in using four or more spatial light modulators may not justify an incremental improvement in color gamut for consumer projection devices. Thus, while the disclosure of application WO 01/95544 teaches gamut expansion in theory, in practice there are a number of significant drawbacks to the design solutions proposed. As a studied consideration of application WO 01/95544 clearly shows, problems that were difficult to solve for 3-color projection, such as timing synchronization, color alignment, maintaining brightness and contrast, cost of spatial light modulators and overall complexity, are even more challenging when attempting to use four or more component colors.
Thus, although there have been some proposed solutions using two or more spatial light modulators for projection apparatus that use three or more colors, there is room for improvement. Lamps and other broadband light sources set practical limits on achievable brightness levels, particularly where color filter wheels or similar devices that cause some amount of light attenuation or have inherent “dead space” during transitions are employed. The use of color wheels makes it unwieldy to alter or adjust illumination timing. In the face of these difficulties, the advantages of expanding the color gamut with an additional color would not be considered within reach using conventional design approaches.
The design of practical 2D/3D switchable displays for home use has not been completely addressed. Additionally, the tradeoff between performance in 2D mode and 3D mode for color gamut and luminance efficiency has not been completely addressed. The system components and design rules governing the means to drive a display in both modes, as well as the rules for placement of emitters in a proper color space are still needed for a viable switchable 2D/3D display system for home use.